A recent animal experiment found that mice exposed to sufficient noise to produce temporary threshold shift (TTS) experienced unexpected, persistent suprathreshold changes in auditory function even though their long-term hearing thresholds remained normal. The results conflict with occupational noise exposure guidelines and regulations, which assume reversible threshold shifts (i.e., TTS) are associated with benign levels of exposure. The purpose of the proposed study is to establish whether the conclusion of the animal experiment is applicable to man and, as predicted, causes impaired speech understanding in noise and/or perturbed perception of loudness growth (LG). We propose to study adult males or females (aged 21 - 50 years) with normal audiometric hearing thresholds (HLs) who either report frequent exposure to noise and/or loud music and symptoms suggestive of noise-induced TTS and/or tinnitus ("exposed" group), or little or no exposure to noise or symptoms suggestive of noise-induced TTS or tinnitus ("unexposed" group). Volunteers will complete a questionnaire to establish symptoms and exposures after confirmation of their HLs. Up to 90 volunteers will participate in behavioral tests of: 1) pure-tone HLs;2) word scores in noise using the Modified Rhyme Test, and;3) thresholds for detecting sinusoidal amplitude modulation of pure tones. The analysis of data will be performed on 25 "exposed" and 25 "unexposed persons selected to best match the group mean audiometric thresholds. The proposal addresses an issue relevant to the Hearing Loss Prevention Cross-Sector Program and all NORA Sector Programs in which hearing loss may occur (Agriculture, Forestry, Construction, Manufacturing, Mining, and Transportation). Confirmation of the need to reduce or eliminate reversible threshold shifts will require intermediate outcomes such as public policy changes concerning occupational noise exposures and hearing conservation programs. There will also be a need for redesigned hearing protectors and improved communication devices to comply with the more restrictive noise exposure guidelines that would be required to reduce hazardous exposures. Identifying the need for such devices would contribute to NIOSH's r2P initiative. Should the effect prove to be experienced by only a few persons, it may be more appropriate to develop devices designed to compensate for a deficiency in the LG function (see Brammer and Bernstein, 2012). Hence, providing a rapid method for establishing the LG function, as proposed here, will contribute to NIOSH's r2P initiative by enabling the development of such devices. The outputs of the proposed research will be presented at conferences and published in scientific journals.

Public Health Relevance

A recent animal experiment found that mice exposed to sufficient noise to produce temporary threshold shift (TTS) experienced unexpected, persistent suprathreshold changes in auditory function even though their long-term hearing thresholds remained normal. The results conflict with occupational noise exposure guidelines and regulations, which assume reversible threshold shifts (i.e., TTS) are associated with benign levels of exposure. The purpose of the proposed study is to establish whether the conclusion of the animal experiment is applicable to man and, as predicted, causes impaired speech understanding in noise and/or perturbed perception of loudness growth.